1. Field of the Invention
The present invention relates to a tire air pressure monitoring system (TPMS) comprising a vehicle-installed device, a portable keyless entry device, and a tire air pressure transmitter, and, more particularly, to a technology for giving a warning when an abnormality in the air pressure of a tire occurs.
2. Description of the Related Art
According to a related technology, a tire air pressure abnormality warning device comprises air pressure sensors for detecting the internal air pressures of tires. Detection signals from the sensors are output from transmitters mounted to wheels, and a receiver in an automobile receives the output detection signals. When an abnormal air pressure of any tire is detected, a warning is given by a driver's indicator panel.
Japanese Patent No. 2716335 discloses a structure in which a receiver, which receives a door lock signal and a door unlock signal from a radio-wave key (operating key), in a vehicle receives an abnormality detection signal from a transmitter that indicates an abnormal state of a tire. It also discloses a technology in which, based on the tire abnormality detection signal, a first warning unit or a second warning unit is selectively driven in order to output a warning inside or outside the vehicle. In other words, by selectively giving a warning inside or outside the vehicle when an abnormality of a tire is detected, the warning is given in accordance with whether a person is in the vehicle or is not in a parked vehicle.
The related technology for giving a warning by a driver's indicator panel causes inconvenience to a driver because, after a warning has been given by the indicator panel, the driver must get out of the vehicle in order to check the actual air pressure of a tire. In particular, when an abnormality in the air pressure of a tire of a parked vehicle is detected, a person cannot confirm any warning unless the person gets into the vehicle and looks at or listens to the driver's indicator panel. Therefore, after confirming the warning, the person must get off the vehicle again and actually check the abnormality of the tire, thereby causing inconvenience to the person.
In addition, in the technology that is disclosed in the aforementioned document, although, when the driver is outside the vehicle, he can know that a tire abnormality has occurred by a warning that is directed to the outside of the vehicle, the driver cannot know that the abnormality has occurred when he is outside a range that allows him to hear the warning.